The invention relates to a transport belt for receiving the ink, not ejected for printing purposes, of an inkjet printer, said belt comprising a carrier layer and a support layer for supporting and printing materials of differing printing width and length by means of an inkjet print head.
An inkjet printer is known from German Patent 39 37 860 C2 issued Jan. 16, 1997 which uses a transport belt for paper sheets, in which by means of a charging device the transport belt and the paper can be electrostatically charged with different polarity so that the paper is fixed on the belt, with the electrostatically charged area of the transport belt being wider than the inkjet print head and larger than the paper length. Thus, ink is ejected between the sheets to be printed and, in the case of blind ejection of ink for removal of air bubbles in the print head, ink is drawn onto the transport belt. To clean the transport belt, the latter has an ink attracting layer, not described in detail, which is cleaned by a pair of removal rollers, likewise not described in detail.
The European Patent 0 269 602 B1 issued Jan. 2, 1992 describes a method for drying of a printed material web in which the latter is fixed in non-slip form on a transport belt, passed with the transport belt in a straight line through the dryer and then lifted off the transport belt. Thus, a material web screen-printed using printing ink can be lifted off the transport belt without smudging. The belt is then subjected to wet cleaning.
The disadvantage of the solutions described is that the ink or dye printed onto the endless transport belts is absorbed by the belt and must then be removed by extensive cleaning before the belt area in question is again ready for receiving a new paper sheet or material web. Depending on the porosity of the belt material used and on the viscosity of the ink, the latter is absorbed at differing speeds and achieves varying penetration depths into the belt material. The cleaning process for removing the ink from the belt is correspondingly extensive. If a specific number of ink printing operations has been performed, the belt attains its ink saturation value, after which no further ink is absorbed and the risk of smudging on the printing material cannot be ruled out.
The object underlying the present invention is to provide a transport belt for receiving the excess ink output from an inkjet printer by which ink sprayed onto the transport belt during the printing of printing material is absorbed such that smudging on the back of the paper is prevented. A further object is to prevent ink absorption of the transport belt in order to achieve a longer service life of the belt than that in the prior art.
In particular, the transport belt for receiving excess ink ejected from an inkjet printer comprises a carrier layer and a support layer for supporting and printing materials, with the support layer comprising a knobbed grid structure with a hydrophobic coating. The coating is formed from a silicone film impervious to water and ink. Since water is used as the solvent for the ink, which can consist of 80% water, a dependable water-repellent or water-tight effect can be advantageously achieved. This offers the advantage, in addition to that of preventing soiling of the transport belt, that the water as solvent for the ink evaporates more slowly and hence drying on the transport belt is slowed down, which considerably facilitates subsequent transport belt cleaning.
The knobs of the transport belt can be configured as truncated cones or truncated pyramids. The design offers in particular the advantage that owing to the geometrical structure of the truncated cones or truncated pyramids the ink collects as a result of gravity on the bottom of the interstices, which can be regarded as a grooved structure, thereby preventing smearing on the back of the printing material being printed. Furthermore, absorption of the ink is prevented by the silicone film. This has the advantage not only of preventing soiling of the transport belt, but also that the water as solvent for the ink evaporates more slowly and hence drying on the transport belt is slowed down, which considerably facilitates subsequent transport belt cleaning.
The geometrical arrangement of the knobbed grid structure results in grid lines at an angle of 45xc2x0 to the transport direction. This advantageously ensures that the leading edge of the printing material is always supported by the knobs over its entire width. The density of the printing material ensures that level contact with the transport belt is assured.